Papers by Keyword: AC Impedance Spectroscopy (ACIS)

Abstract: Highly pure transparent single-crystalline BaTi₂O₅, 6 mm in diameter and 15 mm in length, was prepared by a floating zone (FZ) method using high purity BaCO₃ as a source material. The as-prepared crystal was partially dark blue and became transparent by annealing at 773 K in air. The maximum value of permittivity (ε_max) was 36000 at the frequency of 100 kHz and the Curie temperature (T_C) was 757 K.

Abstract: This article presents a recent study on the behavior of impedance versus frequency of fiber materials. When applying a constant amplitude, it was experimentally observed that the impedance of fiber materials first dropped steeply and then retained in a stable state being followed by a rapid increase with increasing inspiriting signal frequency. The overall impedance versus frequency curve revealed a bathtub-like shape. This behavior is therefore defined as bathtub phenomenon of fiber alternating current (AC) electric conductance. Analysis of the bathtub phenomenon, by using the circuit theory and medium polarization theory, revealed that there exist four different kinds of current in a fiber material when it is exposed to an AC electric field, viz., absorbing current, conductance current, charging current and superficial current. The study showed that this phenomenon is well consistent with and can be evaluated by the medium polarize theory. Understanding of the bathtub effect of fiber AC electric conductance provides a theoretical basis for development of a breaking-through solution to resolve many challenges of conventional impedance technique, such as greatness test error and electrode polarization, etc. The results of this research can be applied to the technology development of novel equipment design for the quick fiber moisture test.

Abstract: Dye sensitized solar cells (DSSC) have been fabricated by using polymer gel electrolyte consisting of ionic liquids in a composite polymers of siloxane and ethylene oxide groups. The structure of those DSSCs are ITO/Ti:ZnO/TiO₂/Ru-dye/gel electrolyte/Pt/ITO, with active area of about 0,5 cm². At this preliminary work, the structure parameters and fabrication procedures had not been optimized for achieving the best performance, but it had been carefully controlled to be same for all fabricated DSSCs. Those DSSCs shows the solar cell performance similar to that observed in DSSCs fabricated in the same cell structure but using conventional electrolyte solution. They exhibit better open voltage and filling factor, which is suggested to the reduction of charge carrier recombination probably taking place at the double layer region formed at the electrode interfaces. This is consistent with their impedance spectrum which is dominated by a Warburg-like characteristics indicating a diffusion limited migration process. It seems then the cell performances is improved by the reduction of charge recombination loss but restricted by diffusion limited ion migration process.

Abstract: This study is focused on the elaboration of 8 mol.% yttria stabilized zirconia (YSZ) thin films onto porous supporting NiOYSZ anode substrates using pulsed laser deposition (PLD),and their microstructural and electrical characterizations. Better crystallinity and grain connectivity is observed increasing the deposition temperature until best values are obtained at 500°C. The greater relative conductivity enhancement is found at 300-500°C. The observed an increased conductivity at lower temperatures may be caused by a combination of nanoscaled effect of the YSZ thin film and interfacial effects between YSZ thin film and substrate.

Abstract: With the growing problem of automobile exhaust pollution, the study of automotive oxygen sensor is very meaningful, nitrogen oxides accounts for a large proportion of automobile exhaust. AC impedance spectroscopy of the NOx sensor in different temperature(500°C，600°C，700°C) and NO2 of different concentrations （100ppm，500ppm，1000ppm）in this paper, the influence of temperature and gas concentration on NOx sensors is explored.

Abstract: As an important and mature technology of researching material properties, ac impedance spectroscopy has successfully applied in many discipline except for soil research. Based on the experiments using TH2828A wide frequency LCR meter (from 50 to 10⁶ Hz), the ac impedance characteristics with different water content of soil had been discussed. The results fully illustrate that the ac impedance is one of the basic property of soil,and the value of ac impedance parameter can be reflected the water content quantitatively. when using the fixed frequency to measure ac impedance of soil, it is most suitable as the frequency equals 10⁴ Hz.The measure method of ac impedance have no effect to physical properties and internal structure of soil.

Abstract: The electrical responses of Zn-Bi-Co-Mn-Ti system low-voltage varistor ceramics were prepared by solid-state reaction method and were analyzed by AC impedance spectroscopy over a wide range of temperature (100~270°C) in the frequency range of 40~13MHz. The equivalent circuit adopts R (RQ)(RC) model. Imaginary part of impedance and modulus with frequency plot exhibits the varistor ceramics including resistance and capacitance. Impedance analysis enables us to separate the contributions from grains and grain boundaries of our samples. It indicates that grain boundary impedance is the main contributor for ceramic resistance, and grain boundary relaxation effects are most obvious in Zn-Bi-Co-Mn-Ti system. The AC grain boundary conductivity activation energy is attributed to the motion of oxygen vacancies within the bulk, and calculated by Arrhenius equation.

Abstract: This experiment composes irreversible cells using ultrafine electrolyte materials and platinum slices, to measure the ionic conductivity the cells at normal temperatures with the help of impedance 1286 spectroscopy. We have calculated the ionic conductivities, which indicate that the ionic conductivities of the merchant LaF3 polycrystalline powder and the powder by microwave method are higher than the ones of LaF3 crystal and the powder by Sol-Gel method, to achieve 10-6 Scm-1, so, they are better ionic conductors at normal temperature and can be used as sensor base materials. The experimental data show that O- participates in ionic conduction.

Abstract: Electrodeless resistivity and impedance spectroscopy measurement are reliable equipments of test online for monitoring the hydration process of cement-based materials continuously and accurately. Phosphoaluminate cement (PAC) sets quickly and develops high early strength. In order to understand the mechanism, the hydration products and microstructure formation of PAC in early age need to be studied. In the study, early hydration process and impedance spectroscopy characteristics of PAC with different dosage of retarder were investigated. According to the test, resistivity of freshly mixed PAC paste decreases sharply and then rises slowly, some characteristic peaks appear at different hydration stages of PAC, which indicates the hydration process of PAC includes four stages which are dissolution, induction, acceleration and deceleration. Impedance spectroscopy can reflect the change of micro-structure and ion concentribution of PAC matrix by resistance and capacitance.

Abstract: b-axis oriented SrO substituted BaTi2O5 (Ba1-xSrxTi2O5) was prepared by arc-melting. The effect of SrO substitution on the dielectric properties of BaTi2O5 (BT2) was investigated by A.C. impedance spectroscopy. The Cole-Cole plot of Ba1-xSrxTi2O5 showed a distorted semi-circle which was deconvoluted into two semicircles corresponding to the bulk BT2 and a second phase. The complex impedance, modulus and capacitances from the ferroelectric bulk matrix and the paraelectric second phase of Ba1-xSrxTi2O5 were simulated by a Maxwell-Wagner model.